1. Field of the Invention
The present invention relates generally to locking devices for releasably fixing two rotating members in a given position with respect to each other, and more particularly to such locking devices as utilize push button release mechanisms.
2. Description of the Prior Art
The use of spring-loaded push buttons as locking devices, to lock a pair of mutually sliding members is well known in the art. In general, such locking pin devices are used with collapsible equipment such as folding walkers and other apparatus specially designed for invalids. Representative appliances utilizing various locking devices are disclosed in the following U.S. Patents: U.S. Pat. No. 3,783,886 to Thomas; U.S. Pat. No. 3,840,034 to Smith; U.S. Pat. No. 3,945,389 to Smith; U.S. Pat. No. 4,056,115 to Thomas; and U.S. Pat. No. 4,180,086 also to Thomas.
Of the patents recited, U.S. Pat. No. 4,056,115 recognizes that the prior art locking devices, comprising spring-loaded push buttons and the like, are difficult to manipulate, particularly by individuals with limited manual dexterity who frequently require the aid of such appliances. The '115 patent makes reference to various approaches that attempted to minimize or overcome the problem with spring-loaded locking pins. Thus, U.S. Pat. No. 3,688,789 is noted, in addition to those listed above, that describes the use of an actuating lever that when pressed against the frame of the walker draws the locking pin out of its locking hole, and permits the telescoping tubular members to slide with respect to each other. The '115 seeks to remedy the aforementioned deficiencies by providing a retrofittably adaptor comprising a sleeve with a reciprocable plunger disposed therein, which is adapted to align with the conventional push button assembly, to permit the user to urge the push button inward by simple palm depression.
Like the prior art devices discussed within its disclosure, the adaptor of the '115 patent provides an inadequate remedy to the basic problem. The disclosed adaptor, when retrofitted, tends to slip in operation, which the result that it can malfuntion in use and thus render the locking mechanism totally inoperable without repair. Further, whether used in a retrofitting capacity, or as part of original construction, the adaptor of the '115 patent does not confer an economy in manufacture of such devices, which is crucial in most instances to the ultimate purchasers thereof. The adaptor of the '115 patent makes use of the conventional spring-loaded locking pin which, by its own design is subject to mechanical failure and jamming in use.
One of the above listed patents illustrates a variation on the approach taken by the '115 patent, in which locking is effectuated between two members that rotate with respect to each other. Thus, U.S. Pat. No. 3,945,389 disloses a collapsible walker utilizing a corner brace extending from the gate leg to the connecting cross brace, the corner brace having a longitudinal slot therein that passes along a shaft mounted in the corner brace to permit the gate leg to pivot with respect to the cross brace in conventional fashion. The locking means comprises a spring loaded pin or button that extends outward from the cross brace and is adapted to engage a corresponding opening or detent in the corner brace, to lock the gate leg in the opened position with respect to the cross brace. A depressible tab is pivotally mounted on the corner brace and is adapted to communicate with the opening that receives the pin from the cross brace, with a dimple or other protrusion that, when depressed, drives the pin inward to permit the corner brace to slide with respect to the cross brace.
While this latter construction differs from that of the '115 patent, it shares the common element of a push button lock that is constructed and operates in the conventional manner, and therefore with the same limitations. Likewise, the exact alignment of the depressible member may vary, and in use, the dimple may wear, so that depression of the pin may be difficult if possible at all, and the invalid may encounter the same mechanical difficulties as with the walker constructions discussed above.
A need therefore exists for a revised lock design, for use with invalid walkers and other apparatus having members rotatable with respect to each other, that is of simple and durable design and operation and is reduced in cost of manufacture.